Even though embodiments of the invention will be described herein in relation to TD-SCDMA, it should be noted that embodiments of the invention may be equally applicable in any scenario with ACK/NACK functionality and variable block size. Thus, the invention is not limited to TD-SCDMA.
TD-SCDMA is one of the four UMTS standards (the others are WCDMA, CDMA2000 and WIMAX). TD-SCDMA is based on TDD (Time Division Duplex) while WCDMA is based on FDD (Frequency Division Duplex). In a 3GPP R99 version, a TD-SCDMA system has a downlink data rate of 384 kbps and an uplink data rate of 64 kbps. In a 3GPP R5 version, HSDPA (High Speed Downlink Packet Access) is introduced into TD-SCDMA, thus the downlink data rate is increased to 2.8 Mbps and the uplink data rate is increased to 384 kbps. In a subsequent 3GPP R7 version, HSUPA (High Speed Uplink Packet Access) is introduced into TD-SCDMA, and as a result, the uplink data rate is increased to 2.2 Mbps. This technology is called as TD-HSUPA, so as to be differentiated from HSUPA in WCDMA.
At a UE (User Equipment) side, when a HSUPA service is established, if there exist physical resources (including uplink TX power, time slot and code channel) on an E-AGCH (Enhanced-Absolute Grant Channel, which is a downlink physical channel and carries the physical sources for the uplink at a current TTI) at a current TTI (Transmission Time Interval, with a value of 5 ms), a MAC layer will construct a data block called as MAC-e PDU based on the physical resources, and transmits the MAC-e PDU on an E-PUCH (Enhanced-Physical Uplink Channel, which is an uplink physical channel and carries an uplink data block MAC-e PDU of the UE) to Node B at the current TTI. After several TTIs, the UE will receive feedback messages via an E-HICH (Enhanced-Hybrid Indication Channel, which is a downlink physical channel and carries the feedback messages ACK/NACK indicating whether the data block MAC-e PDU transmitted on the uplink is successfully decoded or not) which carries ACK/NACK. If the received feedback message is ACK, the MAC layer will flush the MAC-e PDU data block, and if the received feedback message is NACK, the MAC layer will try to retransmit the data block MAC-e PDU when there exist sufficient physical resources.
In the process of the practical test, it is found that the size of the MAC-e PDU data block constructed by the MAC layer has direct relationship with ACK/NACK indicated on the E-HICH. The bigger the MAC-e PDU data block, the harder the receiving of ACK from Node B. In contrast, the smaller the MAC-e PDU data block, the easier the receiving of ACK from Node B.
When it is found at a network side that there exist many big uplink data blocks at the UE, usually more uplink transmission power is allocated to the UE so as to increase transmission success ratio. However, it is unable to solve this problem merely by increasing the uplink transmission power. Generally speaking, (1) if being provided with more uplink transmission power, the UE will construct a bigger MAC-e PDU using a 16QAM mode. However, due to constraints of Node B (there exist some constraints when a network manufacturer allows a current Node B to decode a data block of the 16QAM mode), decoding error will occur even when the uplink TX power of the UE is increased. (2) Due to complexity of the wireless environment, a bigger data block will be affected more than a smaller data block during the transmission. However, it is impossible to solve this problem by increasing the TX power of the UE.